This invention relates to the analysis of thermal properties of coal and more particularly to a method of evaluating the porosities and heat producing capabilities of coal samples by utilizing non-destructive photothermal probing techniques.
Coal is a heterogeneous organic rock having a variable physical structure and chemical composition. Different samples may have different degrees of porosity. Macerals or microscopic inclusions of any of a number of distinct types may be present in varying proportions. Consequently the calorific value or heat producing capability of samples obtained from different mines or different locations in a particular mine may vary substantially. Evaluation of the calorific value or rank of particular samples can greatly facilitate mining, processing, marketing and utilization of coal.
Accurate testing of coal for calorific value by calorimetry or actual combustion of a sample or by quantitative chemical analysis requires time consuming operations under exactingly controlled conditions. A faster, non-destructive procedure would be much more efficient. Further, these conventional techniques do not provide information about variations of thermal properties at different regions of a given specimen unless such regions are separated to enable repetitive testings of a series of minute samples.
The thermal characteristics of coal are significantly affected by variations in porosity. Conventional calorimetry or chemical analysis both inherently correct for such variations but do not, in the absence of still further complications, provide any direct evaluation of the actual porosity of the sample. It would be highly useful in many instances to obtain an evaluation of porosity as such.
A generalized evaluation of the thermally significant properties of a coal sample may be adequate for many routine test purposes. In other cases, such as in technological research and development operations, it would be more useful to obtain a detailed knowledge of such properties including porosity between different small regions of a particular sample, preferably at the microscopic level and at different depths. Imaging of a sample in this manner, using known techniques, is extremely complicated.